Axonal misrouting in obstetric brachial plexus lesions

Obstetric Brachial Plexus Lesion (OBPL) is injury of the nervous network in the
shoulder acquired during labour. This network connects the brain with the arm
and the degree of damage to sensation and muscle strength varies. The current
practice dictates the neurosurgeon to decide whether surgery is necessary based
on the extent of the injury. The necessity for operation and the exact moment
are yet to be elucidated. This is based on the complexity of this type of
nervous injury. Each projection of a neural cell in the arm has different
layers that can be damaged. In the case where all the layers are damaged, a
neurosurgical intervention can contribute to the recovery of as many
connections as possible. In the case that some layers are spared, the injury
can recover spontaneously in general and operation is not needed. Unfortunately
these different degrees of damage are difficult to distinguish initially
because in all cases the neural signal is not passed on. The operation includes
the removal of the damaged part of nervous tissue and reconnection by placing a
healthy piece of nerve extracted from the lower leg in its place. This makes it
quite important to know who can benefit from the operation and who can suffer
damage by it.
The occuring misrouting of the neural projections can be observed as so called
'co-contractions', which means that the function of different muscles is
irreversibly linked. For example the flexion of the elbow can be linked to the
extension, which can be inconvenient for daily activities. We would like to
have a better understanding of this fenomenon. Also in the future this research
can lead to the earlier assessment of the extent of the injury. We believe that
the more errouneous projections are present, the more extensive the injury must
have been.

The objective of this research is to find out to what extent a correlation
exists between axonal misrouting, the extent of the injury and the associated
functional recovery.

First the current state is determined for the 30 unoperated adults with Erb's
palsy. For this purpose the freedom of movement is measured in the shoulder and
elbow and with a few simple tests the strength of a number of muscles is
determined.

The rest of the research consists of two parts. In the first part during
stimulation of the biceps the maximum co-contraction of two other muscles will
be measured. The best place for stimulation will be determined first. Axonal
misrouting is the very reason why this is not easy to find. The places to
measure are the triceps, the extensor of the elbow and deltoid muscle, which
elevates the arm above shoulder level.

In the second part measurements are made in ten muscles simultaneously using
adhesive electrodes to find out if neural projections have branched in those
muscles. This is achieved applying successively a single stimulus to each of
the ten muscles and ten (sensory) nerves. This is followed by measuring the
activity in ten (sensory)nerves during successive stimulation of three sensory
nerves.

The same is also done with 30 controls.

Stimuli can cause an unconvenient feeling but are very safe considering the
many years of experience with EMG. We do not expect any intense stimuli.